Sri Lanka are still to peak at the World Cup, vice-captain Mahela Jayawardene said on Wednesday, as the 1996 champions prepare to tackle Zimbabwe and book a quarter-final spot.

Sri Lanka go into Thursday's game with five points from four games after wins over Kenya and Canada, a share of the points in a washed-out match against Australia and a narrow defeat at the hands of Pakistan.

Jayawardene believes that Sri Lanka's campaign has been energised by Lasith Malinga's belated entry into the tournament after the slingshot seamer missed the matches against Canada and Pakistan with a back injury.

"Lasith coming back into the team has given us a few more options in our bowling attack which is great," said Jayawardene, of Malinga who took a career-best 6-38 against Kenya.

Malinga also took his second World Cup hat-trick during that match.

"I think we can still improve on our batting, try to bat for longer periods and make sure we build partnerships. Even on the field there is always room to improve.

"We are a very hard-working side when it comes to fielding. We just have to keep improving and make sure we make the most of half-chances."

Jayawardene also warned his team not to under-estimate Zimbabwe who still have an outside chance of making the last eight.

Sri Lanka face a potentially tough last match against New Zealand in Mumbai so they can ill afford any upsets against the African nation.

"We rank Zimbabwe with any other team. I think they are a very good all-round side and we know they can be a surprise package so we are not taking anything lightly," Jayawardene said on Wednesday.

Sri Lanka won their first match against Canada by 310 runs before going down to Pakistan by a narrow 11-run margin.

They also beat Kenya by nine wickets before their match against Australia was abandoned due to rain.

Jayawardene said Sri Lanka need to be on their toes to win their last two matches.

"We just want to concentrate on our performances. That's in our control and we will execute a game plan because we know every team is dangerous and have quality players," said Jayawardene, who hit a century against Canada.

"I think we have been consistent, but still there is room for improvement. I think overall we can be happy. It's a long tournament and it's important that we be consistent and keep improving," said Jayawardene.